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Tuesday, March 10, 2009

Chapter 41 - Animal Nutrition

** Note: the text in blue is the notes given in class, and the text in black is given from the website 'course-notes'. Some of the pictures also forward you to videos relating to the surrounding material.**

Overview: The Need to Feed

All animals eat other organisms—dead or alive, whole or by the piece (including parasites).

·In general, animals fit into one of three dietary categories.

1.Herbivores, such as gorillas, cows, hares, and many snails, eat mainly autotrophs (plants and algae).

2.Carnivores, such as sharks, hawks, spiders, and snakes, eat other animals.

3.Omnivores, such as cockroaches, bears, raccoons, and humans, consume animal and plant or algal matter.

oHumans evolved as hunters, scavengers, and gatherers.

·While the terms herbivore, carnivore, and omnivore represent the kinds of food that an animal usually eats, most animals are opportunistic, eating foods that are outside their main dietary category when these foods are available.

oFor example, cattle and deer, which are herbivores, may occasionally eat small animals or bird eggs.

oMost carnivores obtain some nutrients from plant materials that remain in the digestive tract of the prey that they eat.

oAll animals consume bacteria along with other types of food.

For any animal, a nutritionally adequate diet must satisfy three nutritional needs:

A balanced diet must provide fuel for cellular work.

It must supply the organic raw materials needed to construct organic molecules.

Essential nutrients that the animal cannot make from raw materials must be provided in its food.

Concept 41.1 Homeostatic mechanisms manage an animal’s energy budget

·The flow of food energy into and out of an animal can be viewed as a “budget,” with the production of ATP accounting for the largest fraction by far of the energy budget of most animals.

oATP powers basal or resting metabolism, as well as activity and, in endothermic animals, thermoregulation.

·Nearly all ATP generation is based on the oxidation of organic fuel molecules—carbohydrates, proteins, and fats—in cellular respiration.

oThe monomers of any of these substances can be used as fuel.

oFats are especially rich in energy, liberating about twice the energy liberated from an equal amount of carbohydrate or protein during oxidation.

·When an animal takes in more calories than it needs to produce ATP, the excess can be used for biosynthesis.

oThis biosynthesis can be used to grow in size or for reproduction, or it can be stored in energy depots.

oIn humans, the liver and muscle cells store energy as glycogen, a polymer made up of many glucose units.

In addition to fuel for ATP production, an animal’s diet must supply all the raw materials for biosynthesis (the formation of a chemical compound by a living organism).

oGiven a source of organic carbon (such as sugar) and a source of organic nitrogen (usually in amino acids from the digestion of proteins), animals can fabricate a great variety of organic molecules—carbohydrates, proteins, and lipids.

An animal whose diet is missing one or more essential nutrients is said to be malnourished.

Animal nutrition: Nutritional Requirements

An adequate diet supplies three things: fuel in the form of chemical energy, the organics raw materials for biosynthesis, and essential nutrients.

The essential nutrients required by an animal are those that must be obtained in pre-assembled organic for because the animal cannot produce them.

About half of the 20 essential amino acids must be obtained from food. There are also essential fatty acids which animals can not make and must ingest. Nonessential can be made form other substances in the body.

Absorbed nutrients are in the form of monomers.

Vitamins are organic molecules that are required in the diet in small amounts. They are used as co-factors in enzyme-controlled biochemical reactions.

**Minerals, such as calcium and phosphorus, are simple inorganic nutrients that are also required in the diet in small amounts**

5.Absorption is the stage in food processing when the body’s cells take up small molecules from the digestive tract. Cross the cell membrane with transport mechanisms.

·After the food is digested, the animal’s cells take up small molecules such as amino acids and simple sugars from the digestive compartment, a process called absorption.

6.Elimination occurs when the undigested material passes out of the digestive tract.

·During elimination, undigested material passes out of the digestive compartment.

7.Intracellular digestion occurs within a cell enclosed by a protective membrane. Sponges digest their food this way.

8.Extracellular digestion is carried out by most animals; in this type of digestion, food is broken down outside of cells.

·Many simple animals have a gastrovascular cavity, where digestion takes place. These simple animals have a single opening through which food enters and waste is eliminated.

More complex animals have complete digestive tracts (alimentary canals) which are one-way digestive tubes that begin with the mouth at one end of the terminate in the anus at the other.

Concept 41.4 Each organ of the mammalian digestive system has specialized food-processing functions

·The general principles of food processing are similar for a diversity of animals, including the mammalian system that we will use as a representative example.

·The mammalian digestive system consists of the alimentary canal and various accessory glands that secrete digestive juices into the canal through ducts.

oPeristalsis, rhythmic waves of contraction by smooth muscles in the walls of the canal, pushes food along.

oSphincters, muscular ring-like valves, regulate the passage of material between specialized chambers of the canal.

oThe accessory glands include the salivary glands, the pancreas, the liver, and the gallbladder.

·After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested.

·Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours.

·In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.

The oral cavity, pharynx, and esophagus initiate food processing.

Digestion occurs in specialized compartments.

To avoid digesting their own cells and tissues, most organisms conduct digestion in specialized compartments.

·The simplest digestive compartments are food vacuoles, organelles in which hydrolytic enzymes break down food without digesting the cell’s own cytoplasm, a process termed intracellular digestion.

·This process begins after a cell has engulfed food by phagocytosis or pinocytosis.

·Newly formed food vacuoles fuse with lysosomes, which are organelles containing hydrolytic enzymes.

·These tubes are called complete digestive tracts or alimentary canals.

oBecause food moves in one direction, the tube can be organized into specialized regions that carry out digestion and nutrient absorption in a stepwise fashion.

oIn addition, animals with alimentary canals can eat more food before the earlier meal is completely digested.

Step by Step of the Human Digestive System

When food is in the mouth, or oral cavity, a nervous reflex occur which causes saliva to be secreted into the mouth. Saliva lubricates the food and contains the enzymesalivary amylase, which hydrolyzes starch and glycogen into smaller polysaccharides and the disaccharide maltose. This is typically the first type of macromolecules to be enzymatically attacked.

**Know what type of digestion (chemical, etc.) is occurring. Know also where the polysaccharide/monosaccharide is being digested and what is happening**

During chewing, food is shaped into a ball called a bolus. After being swallowed, the bolus enters the pharynx – a junction that opens to the esophagus and the trachea. During swallowing, the epiglottis (a flap made of cartilage) moves to the cover the trachea. This will divert the food to go down the esophagus (also called the alimentary canal).

The esophagus moves food from the pharynx down to the stomach through peristalsis – rhythmic waves of contraction by smooth muscle in the walls of the esophagus (also called the alimentary canal).

The stomach is in the upperabdominal cavity, and its functions include storing food and secreting gastric juice. Gastric juice contains hydrochloric acid, which is very acidic (pH of about 2). Gastric juice breaks down the extra cellular matrix of meat and plant materials, and it also kills most of the bacteria ingested with the food.

Gastrin is a hormone produced by the epithelial lining of the stomach.

Pepsin is an enzyme in gastric juice that begins to hydrolyze proteins into smaller polypeptides. Pepsin is secreted in an inactive form called pepsinogen, which is activated by the hydrochloric acid in the stomach.

The result of digestion in the stomach is a substance called acid chyme. The acid chime is shunted from the end of the stomach into the beginning of the small intestine via the pyloric sphincter.

3 comments:

Oh, sorry when I was on my computer it didn't show the symbols but sometimes when I copy the text from my version of Word to the Blog, it changes some of the bullet points and other points to dollar signs, etc.

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